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The simplest type of tap-changing mechanism is a rotary switch which allows the distribution company to select one of several 'tapping' (connection) points on the high-voltage side of a transformer. This enables the turns-ratio of the transformer to be adjusted to slightly elevate or reduce the output voltage if required. This type of tap changer is termed an 'off-load' tap changer, because it cannot be operated when the transformer is energised because the winding is temporarily disconnected as the mechanism's contacts move from one tap to the next. Off-load tap changers are operated manually, using a handle located outside the transformer -after the transformer has been de-energised, isolated, and safety earths (ground) applied.

More complicated is the motor-driven 'on-load' tap-changing mechanism. It, too, alters the turns-ratio of a transformer, but this is done (usually) automaticallyaccording to changes in load. Unlike the 'off-load' mechanism, the high-voltage winding is never temporarily disconnected as the mechanism's contacts move from one tap to the next. This is because a pair of contacts is involved. One contact moves to the new tap position while the second remains at the first tap connection; when this has been done, the second contact follows the first onto the new tap position -so there is no break in the circuit. Additionally, there might be surge-suppressors fitted, to limit current surges during the tap-changing operation.

Tap changers are always fitted to the high-voltage windings, where the current is lower -thus enabling smaller contacts to be used.

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13y ago
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11y ago

A 'tap' is simply a point of connection on a transformer's winding. Taps are incorporated into transformer windings to allow the transformation ratio to be changed when required, or to provide a range of alternative voltages. For example, in North America, the 240-V low-voltage secondary winding of a single-phase transformer is centre tapped, giving a choice of 120 V (between either outer connection and the centre tap) or 240 V (between the outer connections),

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12y ago

In the context of transmission and distribution Transformers, 'taps' are connections made part-way along a high-voltage winding, enabling minor changes in the transformer's turns ratio to be made, in order to make minor increases or decreases to the secondary voltage to maintain statutory voltage requirements.

A 'tap changer' is the mechanism used to select the appropriate tap settings. Tap changing mechanisms may be 'off load' or 'on load'.

Off-load tap changing can only be performed manually with the transformer disconnected and isolated, as they temporarily disconnect the winding during operation.

On-load tap changing can be performed with the transformer energised and on load, thanks to a 'make-before-break' switching arrangement that ensures the winding is never disconnected when tap changing takes place. On-load tap changing mechanisms are motor driven, and are controlled automatically (with manual over ride when needed).

The tap-changing mechanism is always on the high-voltage side of the transformer, regardless of whether the transformer is step-up or a step-down, because the high-voltage windings carry lower currents, reducing the size of the mechanism's contacts.

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11y ago

* on-load tap changer

* off-load tap changer

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13y ago

A: It is a transformer that has one or more leads wire output so switch can be used to change the output voltage from a reference wire.

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Q: What are the types of tap changing transformer?
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Should the neutral in a service panel be connected to a system ground electrode?

No, the neutral (white wire) should be connected to the center tap of the supply transformer. The electrical service that comes to your home should have 3 wires. Across the 2 black wires should be 240 VAC. That comes from a transformer that steps down from the transmission voltage that is on the high voltage lines. The "center tap" of the output of that transformer gives you 2 legs of the supply, each at 120 VAC. In years past, the center tap has often been connected to ground, but that is no longer the case. The center tap is the neutral connection, and the ground is the part that keeps you from being electrocuted.


What types of roots do tea have?

Tea plants have tap root system


What is the purpose of a transformer?

It steps down voltage by moving the iron core spacing. Mostly using on high current welding transformer. Easy to achieve changing output voltageand does not need to use high power selector to switch voltage


How do you convert 3 phase 415 volts to 208 volts and Is there any electrical diagram or photo if using auto transformer?

Changing the voltage is done by using a transformer. These voltages are dangerous and the job should be done by an electrician who knows the safety regulations that must be followed in your country.


Why can't a transformer step up the voltage in a direct current?

In order to induce a voltage into the secondary winding of a transformer, there must be a continuously-changing magnetic flux within the magnetic circuit (core) linking the secondary and primary windings. This is only possible if the primary current is also changing -hence the reason why transformers require an a.c. supply. There is an exception to this rule -an automobile's ignition coil is a transformer, supplied from the battery -i.e. a d.c. source. But to provide a changing flux, the d.c. current in the primary winding must be continously switched on and off -in older vehicles, this was done by the contact-breaker driven by the distributor.

Related questions

Why was the tap changing panel removed from a transformer?

So that tap-changing can't be done any more, or maybe the tap changer was faulty.


Why tapping is necessary in a transformer?

Taps are connections to the (usually) high-voltage winding of a transformer which enables minor changes to the turns-ratio to be made in order to make minor changes to the secondary voltage to compensate, where necessary, to a fall in terminal voltage below the regulatory allowance.There are two types of tap-changing mechanism, 'off-load' and 'on-load'.Off-load tap-changing mechanisms require the transformer to be isolated before its tap settings can be adjusted, and is normally the case with smaller distribution transformers.On-load tap-changing can be performed with the transformer supplying its load, usually automatically, in response to changes in its secondary voltage. On-load tap changing mechanisms have a 'make before break' switching arrangement, to ensure that the transformer windings are not open circuited during the operation of tap changing.


Why it is necessary to disconnect the load when change the tap?

when the load is connected to draws some current. while changing the tap of the transformer the tappings related to the winding is changed , so the load current affects the transformer. hence while changing the tap it should be noted thatAnswerThere are two types of tap-changing mechanism -'off-load' and 'on-load'. Off-load tap changers physically disconnect the winding when changing from one tap setting to the next. Accordingly, the circuit is temporarily broken, and dangerous arcing will take place if the transformer is energised. Therefore off-load tap changers require that the transformer is disconnected while the mechanism is operated.On the other hand, 'on-load' tap changers use a mechanism which incorporates a 'make before break' contact arrangement, ensuring that no break is made in the circuit as the mechanism moves from one tap setting to the next, enabling it to operate with the transformer energised and supplying load. On-load tap changers are usually automatically operated, although this feature can be overridden and operated manually.


Why there is a need to disconnect transformer while using off-load tap changer?

Changing off-load tap changers requires opening up the transformer, draining (at least some) oil, and manually changing electrical connections. None of these things can be done while the transformer is hot.


What would an off load transformer tap changer be used for?

to inreases or decreases n. of turns of a transformerAnswerAn 'off-load' tap changer is a tap-changing mechanism that can only be used when the transformer is disconnected, as opposed to an 'on-load' tap-changing mechanism that can operate when the transformer is energised and on load.Tap changing is performed to slightly change the turns ratio of a transformer in order to keep the secondary voltage within the statutory limits (e.g. in the UK, 230 V +10% -6%) should there be a substantial change in load.


How is current controlled in welding transformer?

in welding machine, the transformer used is basically a current transforrmer. so by changing the tap of secondary side of transformer, we can increase or decrease the current in the transformer.


How can a step down transformer which is transforming 450 volt in the last tap be changed to 415 volt?

The instruction for changing the taps on a transformer can be found on the transformers nameplate. These taps will be on the primary side of the transformer. Each tap position will state what the voltage will be on the output when the individual tap is selected.


What is no load tap changing in transformer?

It changes the tap while it is operation (hence "on load"). This allows real-time voltage regulation for the transformer secondary (as load picks up, causing the voltage to sag, the LTC can tap up, increasing the voltage).


Why the tap settings are in the secondary of the tap changing transformer?

Usually the voltage at the secondary is the voltage that needs to be controlled. It makes sense, then, to directly control this voltage output instead of controlling the primary.AnswerIt is usual for the tap-changing mechanism to be incorporated into the high-voltage side, regardless of whether the transformer is a step-up or a step-down type. This is because the current is lower on the h.v. side of the transformer and the contacts can be smaller.


What is off load tap change?

Tap changer is a device that is used to change the secondary voltage on transformers. It is normally on the HV winding of the transformer. Off load tap changer is designed to change the taps only when the transformer is not charged, while on load tap changer is capable of changing the tap on load too.


What is center tap transformer?

Center tap transformer is the such kind of transformer that is made to a point half way along a winding of a transformer.


How does the voltage varies through tap chinging of a transformer?

Voltage varies through tap changing of a transformer because the different taps connect to different points on the winding, with the result that use of different taps constitutes use of different turns ratios.